Conventionally, printed circuit boards (PCB) functioning as component carriers comprise a plurality of bores which form vias for generating an electrical connection to an electrical component. Additionally, the bores are used to provide a heat transfer in order to reduce the risk of overheating.
Each component carrier usually comprises a plurality of vias (bores), for example more than thousand. Hence, it is necessary to provide a high-speed bore forming process in order to manufacture the component carrier in a short manufacturing time. Moreover, very small manufacturing tolerances for the size of the bores are allowed in order to provide a proper connectivity. Hence, the high-speed drilling process must not only be fast but must be also very accurate.
Conventional bores need to have a small diameter such that connection pads are kept small and the bores have enough space in the component carrier. However, small sized bores also have less capacity for the heat transfer.
Modern electronic devices are more tiny and precise with even multiple functions, which means that more electronic components have to be placed on a more dense PCB. In case of a laser drilling process, the tight dimension with more components requires smaller laser vias, higher laser via density, tighter line/space design and a smaller capture pad size of a pad connected to a via. However, a tighter line/space design in a limited area leads to a smaller laser via size and connection diameter. Due to laser energy reflection, when hitting an inner layer target Cu (Copper) pad during laser drilling, an over hang around the via (bore) opening is created. Standard plating technology requires laser formed vias with a small aspect ratio AR (=Length A of bore/opening diameter R of bore) typically around 0.8, because otherwise the risk of plating defects such as inclusion and crack will increase significantly.
When laser vias with smaller connection (pad) diameters are required on a dielectric PCB having a same thickness in order to avoid mis-registration (=laser vias shift to an inner layer pad), the opening diameter of a via would have to be also reduced and therefore higher risk of plating effects is given.
A limited PCB dimension to which more and more electronic components are installed means also a higher heat spread and heat transfer requirement. Around 30% of bores (vias) which may be formed by laser drilling will be connected to a ground land and are dedicated for a heat spread function.